The present invention relates generally to anti-fungal peptides derived from or based on Domain III (amino acids 142-169) of bactericidal/permeability-increasing protein (BPI) and therapeutic uses of such peptides.
BPI is a protein isolated from the granules of mammalian polymorphonuclear leukocytes (PMNs or neutrophils), which are blood cells essential in the defense against invading microorganisms. Human BPI protein has been isolated from PMNs by acid extraction combined with either ion exchange chromatography Elsbach, J. Biol. Chem., 254:11000 (1979)! or E. coli affinity chromatography Weiss, et al., Blood, 69:652 (1987)!. BPI obtained in such a manner is referred to herein as natural BPI and has been shown to have potent bactericidal activity against a broad spectrum of gram-negative bacteria. The molecular weight of human BPI is approximately 55,000 daltons (55 kD). The amino acid sequence of the entire human BPI protein and the nucleic acid sequence of DNA encoding the protein have been reported in FIG. 1 of Gray et al., J. Biol. Chem., 264:9505 (1989), incorporated herein by reference. The Gray et al. DNA and amino acid sequences are set out in SEQ ID NOS: 251 and 252 hereto.
BPI is a strongly cationic protein. The N-terminal half of BPI accounts for the high net positive charge; the C-terminal half of the molecule has a net charge of -3. Elsbach and Weiss (1981), supra.! A proteolytic N-terminal fragment of BPI having a molecular weight of about 25 kD has an amphipathic character, containing alternating hydrophobic and hydrophilic regions. This N-terminal fragment of human BPI possesses the anti-bacterial efficacy of the naturally-derived 55 kD human BPI holoprotein. Ooi et al., J. Bio. Chem., 262:14891-14894 (1987)!. In contrast to the N-terminal portion, the C-terminal region of the isolated human BPI protein displays only slightly detectable anti-bacterial activity against gram-negative organisms. Ooi et al., J. Exp. Med., 174:649 (1991).! An N-terminal BPI fragment of approximately 23 kD, referred to as "rBPI.sub.23," has been produced by recombinant means and also retains anti-bacterial activity against gram-negative organisms Gazzano-Santoro et al., Infect. Immun. 60:4754-4761 (1992)!. In that publication, an expression vector was used as a source of DNA encoding a recombinant expression product (rBPI.sub.23). The vector was constructed to encode the 31-residue signal sequence and the first 199 amino acids of the N-terminus of the mature human BPI, as set out in SEQ ID NOS: 251 and 252 taken from Gray et al., supra, except that valine at position 151 is specified by GTG rather than GTC and residue 185 is glutamic acid (specified by GAG) rather than lysine (specified by AAG). Recombinant holoprotein, also referred to as rBPI, has also been produced having the sequence set out in SEQ ID NOS: 251 and 252 taken from Gray et al., supra, with the exceptions noted for rBPI.sub.23. An N-terminal fragment analog designated rBPI.sub.21 or rBPI.sub.21 .DELTA.cys has been described in co-owned, copending U.S. Pat. No. 5,420,019 which is incorporated herein by reference. This analog comprises the first 193 amino acids of BPI holoprotein as set out in SEQ ID NOS: 251 and 252 but wherein the cysteine at residue number 132 is substituted with alanine, and with the exceptions noted for rBPI.sub.23.
The bactericidal effect of BPI has been reported to be highly specific to gram-negative species, e.g., in Elsbach and Weiss, Inflammation: Basic Principles and Clinical Correlates, eds. Gallin et al., Chapter 30, Raven Press, Ltd. (1992). BPI is commonly thought to be non-toxic for other microorganisms, including yeast, and for higher eukaryotic cells. Elsbach and Weiss (1992), supra, reported that BPI exhibits anti-bacterial activity towards a broad range of gram-negative bacteria at concentrations as low as 10.sup.-8 to 10.sup.-9 M, but that 100- to 1,000-fold higher concentrations of BPI were non-toxic to all of the gram-positive bacterial species, yeasts, and higher eukaryotic cells tested at that time. It was also reported that BPI at a concentration of 10.sup.-6 M or 160 .mu.g/ml had no toxic effect, when tested at a pH of either 7.0 or 5.5, on the gram-positive organisms Staphylococcus aureus (four strains), Staphylococcus epidermidis, Streptococcus faecalis, Bacillus subtilis, Micrococcus lysodeikticus, and Listeria monocytogenes. BPI at 10.sup.-6 M reportedly had no toxic effect on the fungi Candida albicans and Candida parapsilosis at pH 7.0 or 5.5, and was non-toxic to higher eukaryotic cells such as human, rabbit and sheep red blood cells and several human tumor cell lines. See also Elsbach and Weiss, Advances in Inflammation Research, ed. G. Weissmann, Vol. 2, pages 95-113 Raven Press (1981). This reported target cell specificity was believed to be the result of the strong attraction of BPI for lipopolysaccharide (LPS), which is unique to the outer membrane (or envelope) of gram-negative organisms.
The precise mechanism by which BPI kills gram-negative bacteria is not yet completely elucidated, but it is believed that BPI must first bind to the surface of the bacteria through hydrophobic and electrostatic interactions between the cationic BPI protein and negatively charged sites on LPS. LPS has been referred to as "endotoxin" because of the potent inflammatory response that it stimulates, i.e., the release of mediators by host inflammatory cells which may ultimately result in irreversible endotoxic shock. BPI binds to lipid A, reported to be the most toxic and most biologically active component of LPS.
In susceptible gram-negative bacteria, BPI binding is thought to disrupt LPS structure, leading to activation of bacterial enzymes that degrade phospholipids and peptidoglycans, altering the permeability of the cell's outer membrane, and initiating events that ultimately lead to cell death. Elsbach and Weiss (1992), supra!. BPI is thought to act in two stages. The first is a sublethal stage that is characterized by immediate growth arrest, permeabilization of the outer membrane and selective activation of bacterial enzymes that hydrolyze phospholipids and peptidoglycans. Bacteria at this stage can be rescued by growth in serum albumin supplemented media Mannion et al., J. Clin. Invest., 85:853-860 (1990)!. The second stage, defined by growth inhibition that cannot be reversed by serum albumin, occurs after prolonged exposure of the bacteria to BPI and is characterized by extensive physiologic and structural changes, including apparent damage to the inner cytoplasmic membrane.
Initial binding of BPI to LPS leads to organizational changes that probably result from binding to the anionic groups in the KDO region of LPS, which normally stabilize the outer membrane through binding of Mg.sup.++ and Ca.sup.++. Attachment of BPI to the outer membrane of gram-negative bacteria produces rapid permeabilization of the outer membrane to hydrophobic agents such as actinomycin D. Binding of BPI and subsequent gram-negative bacterial killing depends, at least in part, upon the LPS polysaccharide chain length, with long O-chain bearing, "smooth" organisms being more resistant to BPI bactericidal effects than short O-chain bearing, "rough" organisms Weiss et al., J. Clin. Invest. 65: 619-628 (1980)!. This first stage of BPI action, permeabilization of the gram-negative outer envelope, is reversible upon dissociation of the BPI, a process requiring the presence of divalent cations and synthesis of new LPS Weiss et al., J. Immunol. 132:3109-3115 (1984)!. Loss of gram-negative bacterial viability, however, is not reversed by processes which restore the envelope integrity, suggesting that the bactericidal action is mediated by additional lesions induced in the target organism and which may be situated at the cytoplasmic membrane Mannion et al., J. Clin. Invest. 86:631-641 (1990)!. Specific investigation of this possibility has shown that on a molar basis BPI is at least as inhibitory of cytoplasmic membrane vesicle function as polymyxin B In't Veld et al., Infection and Immunity 56:1203-1208 (1988)! but the exact mechanism as well as the relevance of such vesicles to studies of intact organisms has not yet been elucidated.
Three separate functional domains within the recombinant 23 kD N-terminal BPI sequence have been discovered Little et al., J. Biol. Chem. 269:1865 (1994)!. These functional domains of BPI designate a region of the amino acid sequence of BPI that contributes to the total biological activity of the protein and were essentially defmed by the activities of proteolytic cleavage fragments, overlapping 15-mer peptides and other synthetic peptides. Domain I is defined as the amino acid sequence of BPI comprising from about amino acid 17 to about amino acid 45. Peptides based on this domain are moderately active in both the inhibition of LPS-induced LAL activity and in heparin binding assays, and do not exhibit significant bactericidal activity. Domain II is defined as the amino acid sequence of BPI comprising from about amino acid 65 to about amino acid 99. Peptides based on this domain exhibit high LPS and heparin binding capacity and are bactericidal. Domain m is defined as the amino acid sequence of BPI comprising from about amino acid 142 to about amino acid 169. Peptides based on this domain exhibit high LPS and heparin binding activity and are bactericidal. The biological activities of functional domain peptides may include LPS binding, LPS neutralization, heparin binding, heparin neutralization or bactericidal activity.
Fungi are eukaryotic cells that may reproduce sexually or asexually and may be biphasic, with one form in nature and a different form in the infected host. Fungal diseases are referred to as mycoses. Some mycoses are endemic, i.e. infection is acquired in the geographic area that is the natural habitat of that fungus. These endemic mycoses are usually self-limited and minimally symptomatic. Some mycoses are chiefly opportunistic, occurring in immunocompromised patients such as organ transplant patients, cancer patients undergoing chemotherapy, burn patients, AIDS patients, or patients with diabetic ketoacidosis.
Fungal infections are becoming a major health concern for a number of reasons, including the limited number of anti-fungal agents available, the increasing incidence of species resistant to older anti-fungal agents, and the growing population of immunocompromised patients at risk for opportunistic fungal infections. The incidence of systemic fungal infections increased 600% in teaching hospitals and 220% in non-teaching hospitals during the 1980's. The most common clinical isolate is Candida albicans (comprising about 19% of all isolates). In one study, nearly 40% of all deaths from hospital-acquired infections were due to fungi. Sternberg, Science, 266:1632-1634 (1994).!
Anti-fungal agents include three main groups. The major group includes polyene derivatives, including amphotericin B and the structurally related compounds nystatin and pimaricin. These are broad-spectrum anti-fungals that bind to ergosterol, a component of fungal cell membranes, and thereby disrupt the membranes. Amphotericin B is usually effective for systemic mycoses, but its administration is limited by toxic effects that include fever and kidney damage, and other accompanying side effects such as anemia, low blood pressure, headache, nausea, vomiting and phlebitis. The unrelated anti-fungal agent flucytosine (5-fluorocytosine), an orally absorbed drug, is frequently used as an adjunct to amphotericin B treatment for some forms of candidiasis and cryptococcal meningitis. Its adverse effects include bone marrow depression with leukopenia and thrombocytopenia.
The second major group of anti-fungal agents includes azole derivatives which impair synthesis of ergosterol and lead to accumulation of metabolites that disrupt the function of fungal membrane-bound enzyme systems (e.g., cytochrome P450) and inhibit fungal growth. Significant inhibition of mammalian P450 results in significant drug interactions. This group of agents includes ketoconazole, clotrimazole, miconazole, econazole, butoconazole, oxiconazole, sulconazole, terconazole, fluconazole and itraconazole. These agents may be administered to treat systemic mycoses. Ketoconazole, an orally administered imidazole, is used to treat nonmeningeal blastomycosis, histoplasmosis, coccidioidomycosis and paracoccidioidomycosis in non-immunocompromised patients, and is also useful for oral and esophageal candidiasis. Adverse effects include rare drug-induced hepatitis; ketoconazole is also contraindicated in pregnancy. Itraconazole appears to have fewer side effects than ketoconazole and is used for most of the same indications. Fluconazole also has fewer side effects than ketoconazole and is used for oral and esophageal candidiasis and cryptococcal meningitis. Miconazole is a parenteral imidazole with efficacy in coccidioidomycosis and several other mycoses, but has side effects including hyperlipidemia and hyponatremia.
The third major group of anti-fungal agents includes allylamines-thiocarbamates, which are generally used to treat skin infections. This group includes tolnaftate and naftifine.
Another anti-fungal agent is griseofulvin, a fungistatic agent which is administered orally for fungal infections of skin, hair or nails that do not respond to topical treatment.
Most endemic mycoses are acquired by the respiratory route and are minimally symptomatic; cough, fever, headache, and pleuritic pain may be seen. Occasionally, endemic mycoses may cause progressive pulmonary disease or systemic infection. Histoplasmosis, caused by Histoplasma, is the most common endemic respiratory mycosis in the United States; over 40 million people have been infected. The disease is noncontagious and ordinarily self-limited, but chronic pulmonary infection and disseminated infection may occur. Pulmonary infection rarely requires treatment, but disseminated infection may be treated with amphotericin B. Coccidioidomycosis, caused by Coccidioides, is a noncontagious respiratory mycosis prevalent in the southwest United States. It also is usually self-limited but may lead to chronic pulmonary infection or disseminated infection. Amphotericin B or miconazole may be given for treatment. Blastomycosis, caused by Blastomyces is a noncontagious, subacute or chronic endemic mycosis most commonly seen in the southeast United States. Most pulmonary infections are probably self-limited. Patients with progressive lung disease or disseminated disease, and immunocompromised patients, may be treated systemically with amphotericin B. Paracoccidioidomycosis, caused by Paracoccidioides, is a noncontagious respiratory mycosis that is the most common systemic mycosis in South America. It may be acute and self-limited or may produce progressive pulmonary disease or extrapulmonary dissemination. Disseminated disease is generally fatal in the absence of therapy. Sulfonamides may be used but have a low success rate. Amphotericin B produces a higher response rate but relapses may still occur.
Cryptococcosis is a noncontagious, often opportunistic mycosis. It is characterized by respiratory involvement or hematogenous dissemination, often with meningitis. A major etiologic agent is C. neoformans. Most pulmonary infections are probably overlooked, but cryptococcal meningitis, which accounts for 90% of reported disease, is dramatic and seldom overlooked. Cryptococcosis is a particular problem in immunocompromised patients; cryptococcal meningitis occurs in 7 to 10% of AIDS patients. The principal symptom of meningitis is headache; associated findings include mental changes, ocular symptoms, hearing deficits, nausea, vomiting, and seizures. Without treatment, 80% of patients die within two years. In meningitis, cryptococci can be observed in India ink preparations of cerebrospinal fluid sediment, and can be cultured from the cerebrospinal fluid. Treatment is generally with fluconazole or the combination of amphotericin B and flucytosine, although amphotericin B does not cross the blood brain barrier.
Aspergillosis is a term that encompasses a variety of disease processes caused by Aspergillus species. Aspergillus species are ubiquitous; their spores are constantly being inhaled. Of the more than 300 species known, only a few are ordinarily pathogenic for man: A. fumigatus, A. flavus, A. niger, A. nidulans, A. terreus, A. sydowi, A. flavatus, and A. glaucus. Aspergillosis is increasing in prevalence and is particularly a problem among patients with chronic respiratory disease or immunocompromised patients. Among immunocompromised patients, aspergillosis is second only to candidiasis as the most common opportunistic mycosis and accounts for about 15% of the systemic mycoses in this group. Opportunistic pulmonary aspergillosis is characterized by widespread bronchial erosion and ulceration, followed by invasion of the pulmonary vessels, with thrombosis, embolization and infarction. Clinically, infection manifests as a necrotizing patchy bronchopneumonia, sometimes with hemorrhagic pulmonary infarction. In about 40% of cases, there is hematogenous spread to other sites. Aspergillosis is also a rare but devastating complication of burn wounds; amputation is often required for cure. Invasive aspergillosis is commonly fatal, so aggressive diagnosis and treatment is required. Blood, urine and cerebrospinal fluid cultures are rarely positive, but fungi can be seen in smears and biopsies. Amphotericin B can be given for treatment.
Mucormycosis is an acute suppurative opportunistic mycosis that produces rhinocerebral, pulmonary or disseminated disease in immunocompromised patients, and local or disseminated disease in patients with burns or open wounds. Infection is caused by fungi in the class Zygomycetes, and include Basidiobolus, Conidiobolus, Rhizopus, Mucor, Absidia, Mortierella, Cunninghamella, and Saksenaea. Rhinocerebral mucormycosis accounts for about half of all cases of mucormycosis. It is one of the most rapidly fatal fungal diseases, with death occurring within 2-10 days in untreated patients. Early clinical signs include nasal stuffiness, bloody nasal discharge, facial swelling and facial pain. The infection then spreads to the eyes, cranial nerves and brain. Pulmonary mucormycosis is nearly as common as rhinocerebral disease and manifests with the same necrotizing and infarction as aspergillosis. Fungi are virtually never seen or cultured from blood, sputum or cerebrospinal fluid. Disseminated mucormycosis may follow pulmonary or burn wound infection. Treatment is with amphotericin B.
Candidiasis is a general term for a variety of local and systemic processes caused by colonization or infection of the host by species of the yeast Candida. Candidiasis occurs worldwide; superficial infections of the skin, mouth and other mucus membranes are universal. Invasive systemic disease has become a problem due to the use of high doses of antibiotics that destroy normal bacterial flora, immunosuppressive agents, and agents toxic to bone marrow, e.g., during cancer therapy. Neutropenia is a major risk factor for Candida dissemination. Candidiasis is also seen among immunocompromised individuals such as AIDS patients, organ transplant patients, patients receiving parenteral nutrition, and cancer patients undergoing radiation treatment and chemotherapy. It is the most common opportunistic mycosis in the world. The most common etiologic agent is Candida albicans. Other infectious species include C. tropicalis, C. parapsilosis, C. stellatoidea, C. krusei, C. parakrusei, C. lusitaniae, C. pseudotropicalis, C. guilliermondi and C. glabrata. Candida albicans is normally found in the mouth, throat, gastrointestinal tract and vagina of humans. Non-albicans species frequently colonize skin. Candida species occur in two forms that are not temperature- or host-dependent. The usual colonizing forms are yeasts that may assume a pseudomycelial configuration, especially during tissue invasion. Pseudomyceliae result from the sequential budding of yeasts into branching chains of elongated organisms.
Candida albicans contains cell wall mannoproteins that appear to be responsible for attachment of the yeast cells to specific host tissues. It has been reported that the mannan portion, rather than the protein portion, of the mannoproteins is responsible for adherence of fungal cells to spleen and lymph node tissues in mice. Kanbe et al., Infection Immunity, 61:2578-2584 (1993).!
C. albicans also binds avidly to extracellular matrix (ECM) proteins such as fibronectin, laminin, and types I and IV collagen, all of which contain heparin-binding domains. This suggests C. albicans may express a heparin-like surface molecule. Adherence of C. albicans to the ECM may be important in the pathogenesis of disseminated candidiasis. It has been demonstrated that heparin, heparan sulfate and dextran sulfate glycosaminoglycans (GAGs) inhibit adherence of C. albicans to ECM and ECM proteins, possibly by a mechanism involving binding of GAGs to ECM proteins, thus masking these selective ligands. Klotz et al., FEMS Microbiology Letters, 78:205-208 (1992).!
Clinically, candidiasis manifests as superficial mucocutaneous infections, chronic mucocutaneous candidiasis, or systemic infection. Superficial mucocutaneous infections can occur in any area of skin or mucus membrane. Thrush, commonly seen in AIDS patients, is characterized by a patchy or continuous, creamy to gray pseudomembrane that covers the tongue, mouth, or other oropharyngeal surfaces and may be accompanied by ulceration and necrosis. Laryngeal involvement results in hoarseness. Esophagitis is often an extension of oropharyngeal disease and may manifest with symptoms of retrosternal pain and dysphagia. Intestinal candidiasis is commonly asymptomatic, but is a major source of hematogenous invasion in immunocompromised individuals. Intertrigo involves the axillae, groins, inframammary folds, and other warm, moist areas, and may manifest as red, oozing or dry, scaly lesions. Infections may occur in other areas, including perianal and genital areas. Paronychia, infection of the nails, often follows chronic exposure of the hands or feet to moisture. Some patients with limited T-cell immunodeficiency develop chronic mucocutaneous candidiasis. These patients suffer from persistent superficial Candida infection of the skin, scalp, nails and mucus membranes.
Most cases of systemic candidiasis are caused by Candida albicans and C. tropicalis, and increasingly, C. glabrata. Clinical manifestations of Candida infection appear mainly in the eyes, kidneys and skin. In the eyes, there may be single or multiple raised, white, fluffy chorioretinal lesions. These lesions are a potential cause of blindness. Involvement of the kidneys includes diffuse abscesses, capillary necrosis and obstruction of the ureters. Infection may result in progressive renal insufficiency. Systemic Candida infection can also manifest as maculonodular skin lesions surrounded by a reddened area; these lesions have an appearance similar to acne but are a major clue to a potentially lethal disease. Other manifestations of systemic candidiasis may include osteomyelitis, arthritis, meningitis, and abscesses in the brain, heart, liver, spleen and thyroid. Involvement of the lungs is also common, but pulmonary lesions are usually too small to be seen on chest X-ray. Finally, Candida endocarditis can occur in patients receiving prolonged intravenous therapy or cardiac valve implants, or in intravenous drug abusers. Fungal lesions appear on the valves, and can embolize and occlude large blood vessels.
Superficial infections are diagnosed by microscopic examination of scrapings or swabs of infected lesions in the presence of 10% potassium hydroxide. Candida organisms can also be seen on gram stain. Endocarditis is diagnosed by blood cultures or demonstration of bulky valvular lesions on echocardiography. Systemic candidiasis may be difficult to diagnose because the presence of heavy colonization at the usual sites of infection indicates, but does not prove, that dissemination has occurred. The most reliable evidence of systemic candidiasis is biopsy demonstration of tissue invasion or recovery of yeast from fluid in a closed body cavity, such as cerebral spinal fluid, pleural or peritoneal fluid. Similarly, positive blood or urine or sputum cultures may indicate invasive disease or simply localized disease around indwelling devices, e.g., catheters or intravenous lines.
Mucocutaneous infections may be treated with topical preparations of nystatin, amphotericin B, clotrimazole, miconazole, haloprogin or gentian violet. Oropharyngeal or esophageal candidiasis can be treated with systemic agents such as ketoconazole or fluconazole. Chronic mucocutaneous candidiasis syndrome may respond to topical or systemic therapeutic agents such as amphotericin B or ketoconazole, but often relapses when medication is discontinued. Cystitis may be treated with amphotericin B bladder rinses, or a brief low-dose intravenous course of amphotericin B with or without oral flucytosine. Endocarditis is essentially incurable without valve replacement, accompanied by a 6 to 10 week course of amphotericin B and flucytosine. Even with therapy, however, complete cure of endocarditis is not always possible.
The mortality rate from systemic candidiasis is about 50%. Systemic candidiasis may be treated with fluconazole, a fungistatic agent, or amphotericin B, a fungicidal agent although systemic use of the latter is limited by its toxicity. Both drugs have substantial adverse reactions when used in combination with cyclosporine A, which itself can be nephrotoxic. The removal of precipitating factors such as intravenous lines or catheters is also important for controlling infection. Flucytosine therapy can be added to the amphotericin B therapy for treatment of systemic candidiasis, especially in patients that are not immunocompromised. In immunocompromised patients, however, these infections are problematic and resist effective treatment. Mortality with systemic candidiasis can be over 90% in such patients. Furthermore, chronic mucocutaneous candidiasis and candidal endocarditis often show evidence of disease after having been declared cured.
There continues to exist a need in the art for new anti-fungal methods and materials. In particular, effective anti-fungal therapy for systemic mycoses is limited. Products and methods responsive to this need would ideally involve substantially non-toxic compounds available in large quantities by means of synthetic or recombinant methods. Ideal compounds would have a rapid effect and a broad spectrum of fungicidal or fungistatic activity against a variety of different fungal species when administered or applied as the sole anti-fungal agent. Ideal compounds would also be useful in combinative therapies with other anti-fungal agents, particularly where these activities would reduce the amount of anti-fungal agent required for therapeutic effectiveness, enhance the effect of such agents, or limit potential toxic responses and high cost of treatment.